Heat treating method and apparatus for sheet or web material



Dec. 7, 1965 H. L. SMITH, JR HEAT TREATING METHOD AND APPARATUS FORSHEET OR WEB MATERIAL Filed May l5, 1962 vtm mmv

INVENTOR Horace L.Smi1h, dr. Wwf@ ATTORNEYS United States Patent O3,221,416 HEAT TREATING METHD AND APPARATUS FR SHEET R WEB MATERIALHorace L. Smith, Jr., Richmond, Va., assigner to Hnpp Corporation,Cleveiand, Ohio, a corporation of Virginia Filed May 15, 1962, Ser. No.194,879 6 Claims. (Cl. 3i-41) This invention relates to a method of, andapparatus for, the heat treating and drying of continuous sheet, or web,material, and more particularly to a method and apparatus for dryingpaper base materials while under lateral tension. It has particularapplicability in drying relatively thick paper products such forexample, as paper base box board and the following description will bemade in this connection although the invention has general applicabilityas hereinafter set folth.

Box board or the like is normally made on cylinder machines in which aconventional arrangement of rotating cylinder driers receives and driesthe newly produced wet sheet material while maintaining continuousContact with the smooth surface of the driers to prevent wrinkles,cockle, etc. In such apparatus the sheet material is under considerablelongitudinal tension, i.e., tension in the direction of travel, andunder no appreciable laterial tension, i.e., tension in the sheetmaterial at right angles to the direction of sheet travel. Lateralshrinkage is therefore disproportionately large in relation tolongitudinal shrinkage and the resultant product does not exhibitoptimum physical strength and durability in service.

Previous drying methods have also been undesirably slow in productionand many have failed to uniformly heat the entire surface of the wetsheet sufficiently to produce a completely satisfactory Ihigh quality,yet low cost, product.

These and other disadvantages are overcome by my present inventioninvolving maintenance of lateral tension in the wet sheet material afterit has been dried to withstand the tension, and applying heat uniformlyover the entire width of the sheet, preferably by radiation as set forthbelow. As a result, primarily of the lateral tension established in thewet sheet during drying, a product having properties superior to similarproducts heretofore produced, is achieved without substantial, if any,increase in manufacturing costs. The physical or chemical mechanism bywhich the lateral tension produces the improved product overconventional drum drying processes is not known at this time although itis lthought that the results are due to a resultant unique libreorientation, due perhaps to a balancing of the lateral versuslongitudinal shrinkage differential, possibly with the combination ofrelatively fast, uniform heating by radiation which, for best results isby peak radiation in the wave length most readily absorbed by the wetsheet.

The lateral tension created in the wet sheet should be of sufficientmagnitude to prevent wrinkling or cockling, and permit substantially nolateral sagging. Beyond this however, the limits of tension magnitudefor optimum process results can be established by test 4runs for eachmaterial being treated since this will vary basically, according to theorganic composition and thickness of the sheet material, and the degreeof wetness upon entering the dryer. The tension if desired, may bemaintained throughout subsequent treating phases such as cooling orduring application of finishing materials such as treating liquids,although this is not necessary.

The most pertinent art of which I am aware is not in the paper dryingart, but has to do with the heat treatment of textiles, where it hasbeen the practice for a number of years in the iinishing of some typesof cloth, to mount wet cloth on a tentering machine having edge-grippingclips on opposed chains which grip its opposite longitudinal edgeswhereby the cloth is stretched transversely while it 3,22 l ,4 l 6Patented Dec. 7, 1 965 ICC travels in a longitudinal direction throughthe tentering machine. During such travel of the cloth on the machine itis usually heated to dry, set, and cure. The object of lateraltensioning the cloth is to suitably stretch knit goods, prevent weavedeformation, maintain absolute uniformity in width, and to promoteuniformity of treatment to reduce the possibility of streaking orshading. Thus, while the tenter apparatus is somewhat similar to theapparatus disclosed herein, the present invention differs significantlyfrom the tenter treating methods in that the primary purpose here is toproduce a product of improved physical strength, yand having otheradvantages, as well as to promote uniformity and economy of heattreatment. Prior to this invention it has not been thought desirable, orpossible to dry paper base materials in a tenter-like apparatus,primarily because the advantages of drying under lateral tension werenot realized and since it has not heretofore been realized that paperbase materials not having the fiber strength of textiles could behandled for drying on such apparatus.

Accordingly, it is the primary object of this invention to provide anovel method for the production of paper base sheet materials ofimproved physical properties.

Another object is to provide a novel method of producing improved paperboard sheet material such as used in the manufacture of boxes and likemat-erials, by establishing lateral tension in the sheet material whileit is being heated in a suitable heating zone, the source of heat inwhich is preferably, although not necessarily, radiant heaters.

Still another object is to provide novel apparatus and methods forproducing paper board sheet and like materials by establishing laterialtension in the sheet While in a relatively wet state, but after physicalproduction thereof and preliminary drying by conventional apparatus, andthereafter or during application of the laterial tension passing the wetsheet under tension through a heating zone heated preferably, by radiantheaters emitting radiations of peak wave length in the range mostreadily absorbed by said wet sheet.

Other object-s and advantages of the present invention will becomeapparent to those skilled in this art from the appended claims `andfollowing description of the preferred embodiment of the presentinvention taken in connection with the accompanying drawing in which:

FIGURE l is a plan view of a drying apparatus constructed according tothe present invention;

FiGURE 2 is a front elevation View of the apparatus illustrated inFIGURE l;

FIGURE 3 is a detail front elevation view, of larger scale than FIGURESl and 2 of a wet sheet gripping device attached to a piece of sheetmaterial and utilized in the apparatus illustrated in FIGURES l and 2;and

FIGURE 4 is a plan view of a series of gripping devices illustrated asbeing attached to a sheet of material passing through the apparatusillustrated in FIG- URES l and 2.

Referring to the drawing, a conventional box board making machine 10 isdiagrammatically illustrated by phantom lines producing a continuoussheet of wet paper base material 14. A large preheating drum 18 receivesthe wet paper emerging from machine 10 to remove a sufficient amount ofmoisture to enable the wet material to be laterally tensioned and driedin accordance with this invention. Drum 18 is associated with a pair ofguide rollers 22, 23 which direct the wet sheet onto and off of drum 18,and onto another pair of guide rollers 24, 28.

Drum 18, pivoted about shaft 32, may be of any suitable dryingapparatus, for example, a conventional Yankee drier or the like.However, it is preferred that such drying drum be constructed inaccordance with the principles of the invention set out in my copendingapplication Serial No. 118,439, tiled June 20, 1961 for Heat Transferand Pressure Applying Apparatus and Method of Manufacture Thereof (nowPatent No. 3,181,605) wherein a drum is described having aunidirectional, or countercurrent channels, set up therein forreceivinga heated fluid. The latter is preferably a high boiling hydrocarbonliquid capable of being heated to temperatures in the order of S50-700F., without substantial increase in pressure. This rhas considerableadvantage over similar prior art devices in which steam has normallybeen used as the heating medium requiring construction of heatingequipment capable of withstanding relatively high pressures and yetproducing only moderately high temperatures at practical operatingpressures.

As the wet sheet material enters the tensioning and drying zone, it ispassed between radiant heating panels 40 and 42 which are preferablyprovided with the heated, low boiling point liquid which may also becirculated therein in a unidirectional manner, or in channels whichdirect the liquid in opposite, countercurrent directions to therebyachieve a more uniform temperature over the surface of the panel. Aplurality of panels may be connected in series or one single large panelmay be used. However, if a large panel is used, it is desirable that thecountercurrent liquid iiow be utilized inasmuch as the temperature dropover a large panel will be substantial. The heating iiuid mediumsupplied to the panels is suitably heated and pumped in a system inwhich the panel constitutes a part thereof and the liquid is circulatedthrough the panels and recirculated back to the heater and pumpedcontinuously so that the heat may be maintained relatively constant ifdesired. Any suitable system which accomplishes this result may beutilized and it is nota part of this invention.

The radiating panels are preferably, although not necessarily spacedapproximately equal distances from the opposite sides of wet sheet 14.The radiating surfaces of the panels facing the sheet are coated with ahighly emissive material so that the panels may radiate at optimumefficiency. Such emissive material may be for example, a glass fritcoating, or other suitable composition.

Many materials absorb radiation of predetermined wave lengths much morereadily than radiation of other wave lengths. The more radiationabsorbed by a material, the less it reflects, the more heat is generatedtherein, and the quicker the material will be dried to the desireddegree. Accordingly, the radiating surface of the panels are providedwith a coating, and are operated at a temperature, which will emitradiant energy at the wave length range most readily absorbed by theparticular wet sheet material being processed. The selection of asuitable wave length will be dependent on the nature of the wet contentof the sheet material, and the composition of the sheet material itself.If wave lengt-h data is unknown, the optimum wave length range canreadily be determined by known testing methods.

Sheet 14 is carried through the radiant heating Zone by means of atenter apparatus comprised of a pair of chain-like travelingsheet-gripping members indicated generally as 44 and 46 in FIGURE 1, Assheet 14 emerges from roller 28, travelling from left to right as viewedin FIGURE l, it is directed into gripping members 44 and 46 which gripthe sheet material and carry it throughout the length of the heatingzone and deliver it to a final guide roller 50 and product accumulatordiagrammatically illustrated at 54.

Gripping members 44 and 46 are shown substantially parallel in FIGURE 1;however, they may be adjusted to converge or diverge as desireddepending upon the degree of tension desired to be established in thesheet material as it proceeds through the drying zone. Each grippingmember 44 and 46 is comprised of a continuous chain-like element drivenby any suitable means, about sprockets located at the opposite ends ofeach of the gripping members.

The preferred construction of the tenter frame assembly is illustratedin more detail in FIGURES 3 and 4. FIGURE 3 is a detailed showing of thepreferred means by which the gripping members engage and hold movingsheet 14 by a plurality of clamps each comprised of a pair of clamp arms58 pivotally mounted on a U-shaped link body member 59. Clamp arms 58have substantially flat parallel clamping surfaces which engage sheet 14when the clamp is in the closed position as illustrated in full lines inFIGURE 3, and are biased toward a normal open position illustrated indotted lines in FIGURE 3 by a spring member 62 and are closed byrotatable cam followers 66 mounted on each clamp arm 5S and adapted tobear against stationary cam tracks 68 and 70.

Cam tracks 68 and 70 are elongated members having recesses 74 at spacedintervals on the inner side thereof facing `sheet material 14. A guidewheel 76 and 78 is mounted for rotative movement on the top and bottomportions of each chain link body member 59. As the chain moves with thesheet material in its direction of travel, wheels 76 and 78 bear againstthe surface of cam tracks 63 and 'i0 respectively and thereby maintainthe desired path of travel of the chain. Cam followers 66 rolling on theinner side of cam tracks 68 and 70 and being biased against the cam bysprings 62, maintain clamp elements 58 in their closed position until acam follower 66 arrives at a recess 74, at which time the particularclamp arms, associated with the cam, open to the dotted line position asshown in FIGURE 3, and as illustrated by the middle clamp in FIGURE 4for example. Thus, during the travel of the sheet material throughoutthe length of the heating zone it will be engaged by a plurality ofclamps which grip and tend to maintain the width of the sheet materialthe same throughout the drying zone even though it may tend to shrinkdue to drying. However, so that the sheet material will not be undulystressed for too long a period of time the clamps are closed andreleased periodically throughout their travel through the heating zoneaccording to the spacing of recesses 74 along cam tracks 68 and 70.

As the sheet material 14 enters the drying zone, it is initially grippedby a plurality of clamps and as the material proceeds through the dryingzone increased tension will be progressively applied to the sheetmaterial due to its drying and shrinking. Thus, when the grippingmembers 44 and 46 are maintained in a relatively parallel position asshown in FIGURE 1 the extent of tensioning will be directly proportionalto the extent of shrinkage. By maintaining the same width of thematerial from the beginning to the end of the drying zone the forces oftension being applied from within the sheet material, a desirable fibrestructure is established which produces the aforementioned superiorproduct. However, if desired, the degree of tension may be applied byarranging the gripping elements so that they diverge or convergeprogressively through the drying zone. Alternatively, if a maximumtension is desired to be maintained after having once been achieved inthe paper, the gripping elements may be parallel for a portion of therun and then may have intermediate sprockets or other suitable means foreffecting divergence or convergence of the gripping elements throughoutthe remaining length of the drying Zone as desired.

The invention may be embodied in other specific forms without departingfrom the lspirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. A method of producing box board and similar relatively thick paperproducts of improved quality, comprising the steps of:

(a) forming a wet, continuous web of the paper product;

(b) continuously moving the Wet web in at least one horizontal dryingpass between radiant heaters baving emitting 4surfaces substantiallyparallel to, closely adjacent, and on opposite sides of the wet web tothereby dry said Web; and

(c) as the web moves between said radiant heaters,

periodically and alternately;

(d) applying tensile forces acting at right angles to the Webs directionof movement to said product to produce lateral tension therein; and

(e) releasing the lateral tension thereby produced in said web from theweb.

2. The method as defined in claim 1, together with the step of removingfrom the newly formed wet web before it reaches said horizontal dryingpass a minor proportion of the water in said product.

3. The method as defined in claim ll, wherein the lateral tensionapplied to the product is progressively increased as the web movesthrough said horizontal drying pass.

4. The method as dened in claim 1, wherein the lateral tension appliedto said sheet is prevented from exceeding a predetermined maximum assaid web pro gresses through the drying pass.

5. Apparatus for drying box board and similar relatively thick paperproducts under lateral tension to produce products of improved quality,comprising:

(a) means for forming a continuous wet web of the paper product;

(b) preliminary drying means for removing a minor amount of the moisturefrom the newly formed product;

(c) drying means comprising radiant heaters adapted to have the webbeing dried passed therebetween; and

(d) means for conveying the wet Web from the preliminary drying meansthrough the drying means between said radiant heaters, including:

(e) means for, concomitantly with the passage of the web between saidradiant heaters, alternately:

(f) applying tensile forces acting at right angles to the webs directionof movement to said product to produce lateral tension therein; and

(g) releasing the lateral tension thereby produced in said web from theweb;

(h) said last-na1ned means including means for pe riodically applyingsaid tensile forces to and releasing the lateral tension from said webas it passes between said radiant heaters.

6. Apparatus for drying box board and similar relatively thick paperproducts under lateral tension to produce products of improved quality,comprising:

(a) means for forming a continuous wet web of the paper product;

(b) preliminary drying means for removing a minor amount of the moisturefrom the newly formed product;

(c) drying means comprising radiant heaters having parallel, closelyspaced, horizontally Ioriented emitting surfaces at least equal in widthto the width of the web of newly formed product;

(d) means for conveying the newly formed product from the preliminarydrying means through the heated zone between the radiant energy emittingsurfaces and for maintaining lateral t-ension in said web as it movesthrough said zone including means gripping both edges of said webproduct and maintaining a predetermined distance between said edges,said conveying means comprising:

(e) endless members on both sides of the heated zone supported formovement therealong and gripping means comprising:

(f) co-operating upper and lower clamp arms pivotally fixed to saidendless members at predetermined intervals;

(g) spring means biasing said clamp arms apart;

(h) co-operating upper and lower cam tracks extending the length of theheated zone on opposite sides thereof; and

(i) cam followers fixed to said upper and lower clamp arms and engagingsaid upper and lower cam tracks;

(j) said cam tracks being contoured to force said clamp arms againstsaid web against the bias of; the spring means to secure the webtherebetween as it moves through the heated zone.

References Cited by the Examiner UNITED STATES PATENTS 2,094,111 9/1937Willis 34-158 2,103,110 12/1937 Dickhaut 34-158 2,569,713 7/1951 DunskiBIL-158 2,621,422 12/1952 Deck 34-158 2,760,410 8/1956 Gillis 34-182,788,841 4/1957 Hockett 34--158 WILLIAM F. ODEA, Primary Examiner.NORMAN YUDKOFF, Examiner,

1. A METHOD OF PRODUCING BOX BOARD AND SIMILAR RELATIVELY THICK PAPERPRODUCTS OF IMPROVED QUALITY, COMPRISING THE STEPS OF: (A) FORMING AWET, CONTINUOUS WEB OF THE PAPER PRODUCT; (B) CONTINUOUSLY MOVING THEWET WEB IN AT LEAST ONE HORIZONTAL DRYING PASS BETWEEN RADIANT HEATERSHAVING EMITTING SURFACES SUBSTANTIALLY PARALLEL TO, CLOSELY ADJACENT,AND ON OPPOSITE SIDES OF THE WET WEB TO THEREBY DRY SAID WEB; AND (C) ASTHE WEB MOVES BETWEEN SAID RADIANT HEATERS, PERIODICALLY ANDALTERNATELY; (D) APPLYING TENSILE FORCES ACTING AT RIGHT ANGLES TO THEWEB''S DIRECTION OF MOVEMENT TO SAID PRODUCT TO PRODUCE LATERAL TENSIONTHEREIN; AND (E) RELEASING THE LATERAL TENSION THEREBY PRODUCED IN SAIDWEB FROM THE WEB.